Extraction of animal glue in presence of insoluble basic substance



United States Patent'O 12 Claims. (Cl. 260-118) This invention relates to the extraction of animal glue in the presence of an insoluble basic substance.

A method of extracting animal glue in the presence of an insoluble acid-neutralizing material is disclosed in the co-pending application United States Serial No.

acidic pH by having calcium carbonate distributed in the water.

In this process, the porous pieces of collagen-bearing material, such as hide trimmings, are maintained at an acidic pH interiorly during the extraction of the glue therefrom, while at the same time the surrounding water is maintained at an approximately neutral pH. 'This has a two-fold advantage in permitting the glue to be extracted under acid conditions which are known to facilitate the extraction of the glue, while at the same time preventing the extracted glue from having its viscosity impaired by being subjected to an acidic pH. The only disadvantage to the process is that the hydrochloric acid which diffuses out of the glue stock solids reacts with the calcium carbonate to form soluble calcium chloride. The presence of the dissolved calcium chloride in the glue liquors is undesirable. Calcium chloride is hygroscopic and may pick up suflicient moisture from the air to impart tackiness to the glue. Moreover, calcium chloride and other inorganic salts act as dejelling agents for glue, and also tend to adversely'afiect the viscosity of glue. Therefore, a glue of low ash content or low inorganic salt content is preferred.

It is the principal object of this invention to provide a process wherein glue can be extracted from acidulated glue stock into water at a non-acidic pH, without increasing the inorganic salt content of the extracted glue. Further objects and advantages will appear as the specification proceeds.

It has been discovered that the above object can be achieved by employing a water-soluble acid for acidulating the glue stock solids and a water-insoluble basic substance for maintaining the neutrality of the extracting water, which are characterized by the fact that the water-soluble acid will react with the water-insoluble basic substance to form a water-insoluble salt. Specifically, it has been found that these results can best be achieved when calcium carbonate or other alkaline earth metal carbonate is employed as the insoluble basic compound, as preferred, by using oxalic acid to acidify the glue stock solids.

The starting material for use in the process of this invention can, be any collagen-bearing animal tissue.-

The process is well adapted for use with hide glue stock,

and especially cattle hide glue stock. The two main types of cattle hide glue stock are (a) trimmings from salt-cured cattle hides and (b) fresh cattle hides such as the ears and lips. The process can also be advantageously employed with bacon skins as the starting mate rial.

The collagen bearing tissue can be conditioned according to standard practice by soaking in a saturated lime solution for 60 to 120 days, depending on the temperature conditions. Alternatively, it can be conditioned by the enzymatic action of yeast, particularly Mycoderma' and Torulopsis, as described in detail in co-pending application, United States Serial No. 339,166, filed February 26, 1953, for. Method of Preparing Animal Glue.

The completely or partially conditioned glue stock can then be treated in an acid bath, for example, in.

water at a pH below 6.5, and preferably at a pH from 1.5 to 6.0. In the commercial practice, the limed hides are generally treated with water at a pH of aroundv 6.0, although in connection with the extraction method of this invention it probably would be desirable to employ somewhat lower pHs in this step. In the co-pending application, cited above, the microorganism-conditioned hides are soaked in water at a pH from 1.5 to 3.5 to.

swell the hides. As indicated therein, pHs of from 2 to 2.5 are preferred, since the swelling has been found to be at a maximum of around 2.3. In the acid-treating or swelling step, various acids can be employed, but hydrochloric acid is preferred. Instead of hydrochloric acid other acids can be employed, such as nitric acid, sulfuric acid, acetic acid, phosphoric acid, etc.

Following the acid swelling of the glue stock, or as a continuation of the acid swelling, it is preferred to replace the hydrochloric acid or other acid mentioned above with an acid which, when reacted with calcium carbonate or other water-insoluble basic substance fall-.

ing within the scope of this invention as described below,

- will form a water-insoluble salt, thus permitting it to be separated from the extracted glue by physical separating procedures such as filtration and centrifugation. Oxalic acid has been found to be advantageous for this purpose. If desired, the cattle hide trimmings or other glue stock can be acidulated entirely with an aqueous solution of oxalic acid, or, as preferred, it can first be subjected to an initial swelling as described above with hydrochloric acid or other strong mineral acid, and thenthe strong mineral acid replaced in the tissue solids with oxalic acid. This can be done by separating the solids from the hydrochloric acid bath and washing them with an aqueous solution of oxalic acid. Alternatively, the separated glue stock solids can be washed with water and then soaked in an oxalic acid solution. A pH of from 2 to 2.7 can readily be obtained with dilute oxalic-:1

acid solutions. a

The acidulated glue stock can then be directly extracted without neutralization by the method of this invention. However, it is desired to separate the tissue solids, as much as possible, from the acid-treating liquid. This can readily be done by draining or centrifuging, followed by a brief water rinse. obtained will be at the acidic pH employed in the swelling treatment. These tissue solids are then suspended in water containing an insoluble basic compound, such as calcium carbonate. Any insoluble acid-neutralizing material which will react with the acid contained within the tissue solids to form a water-insoluble salt can be employed. However, the alkaline-earth metal carbon ates, and particularly calcium carbonate, have been found to give best results. Water-insoluble basic oxides, such .as aluminum oxide (A1203), can be substituted for.ca1-- cium carbonate, providing they will react with the acid l employed to form a water-insoluble salt.

Instead of oxalic acid other acids having the stated ,tcharacteristics can be used. For example, the alkaline Patented Apr. 3, 1 956 The tissue solids thus earth metal salts'of common acids such as sulfuric, phosphoric, sulfurous, citric, etc., are quite insoluble in water; and therefore these acids can be used for the internal acidification of the glue stock solids, while the glue liquors are neutralized withbasic water-insoluble alkaline earth metal compounds, such as the alkaline earth metal carbonates.

It is preferred to employ the insoluble basic materialin' apnlverized or finely-divided condition so that-it can be distributed throughout the extraction bath. l tis also desirable to employ an excess of the insoluble basic material, that is, it is desired to-use more of it than is required to neutralize the acid which is extracted with-the glue. If the glue stock is to be subjected to a series of cooks, it will usually be necessary to employ somewhat more insoluble basic material in the first cook thanin the succeeding cooks, since more acid will'be extracted inthe first cook. There is no particular disadvantage to using a considerable excess of the insoluble basic materiaLsince it has been found that it can readily'be separated from the glue liquor by centrifugation or filtration. During the extraction, the glue is extracted under the acid conditions within the solid pieces of tissue, but as soon as the acid diffuses out of the tissue it is'neutralized byreacting with the insoluble basic material, thus maintaining non-acidic pH conditions for the extracted glue and thereby preventing its viscosity from being impaired. In the process, the extracted glue acts as a dispersant for the particles of the insoluble acid-neutralizing material, and therefore these particles willbe well distributed throughout the bath and readily available for-neutralization ofthe extracted acid. When aninsoluble carbonate is used, as preferred, the carbon-dioxide evolved in theneutralization serves the further purpose of agitatingthe mixture. Apparently the insoluble base particles do not appreciably enter the tissue, since the interior of'the' pieces of glue stock can be maintained at an acid pH for a series of cooks in the presence of an insoluble base. The water-soluble acid, such as oxalic acid, reacts with the water-insoluble basic compound, such as calcium carbonate, to form a water-insoluble salt, such as calcium oxalate. The water-insoluble salt thus formed can be readily separated from the glue liquors by centrifugation or filtration together with any excess of the insoluble base.

In the glue extraction step, conventional temperatures can be employed, that is, temperatures ranging from 65 to 100 C. By way of specific example, theglue stock-might be extracted four times by covering it with water having the insoluble base therein, and subjecting it to a series of'3-hour cooking periods at 65",

75-, 85, and 100' C The glue liquor obtained in this manner can then beseparated from any excess-of insolu ble base and the insoluble salt by centrifugation orfiltration.

This invention is illustrated by the following specific examples.

Example I Cattle hide trimmings, washed substantially free of salt, blood,.excreta, debris, etc., were conditioned for 3 days .in hydrochloric acid solution at pH 4 in the presence of sodium silicofluoride and native yeast cultures. During this period the conditioning bath temperature was maintained at 37 C. The conditioned hide trimmings were removed from the conditioningbath and placed in 4 Example ll Low ash glues were prepared from acid swelled bacon skins by the following process.

Bacon skins, washed substantially free of salt, were swelled for 4 to 8 hours in dilute (OZ-2.0%) oxalic acid. The acid-swelled material. was then placed in water for glue extraction. Calcium carbonate was added to the water and the glue was extracted in repetitive cooks. The excess calcium carbonate and insoluble calcium oxalate were removed and the glue liquor dried, after .re moval of fat by skimming or centrifuging. In this way, a high quality, low ash glue was obtained in a high yield.

Example. III

Cattle hide trimmings washed substantially free of salt, blood, excreta, debris, etc., were conditioned for three days in an aqueous solution of sodium silicofiuoride in the presence of native yeasts and added. yeast cultures.

During this period the conditioning bath was maintained.

at 37 C. The conditioned material was drained free of the conditioning solution and was then immersed in a dilute solution of sulfurous acid at pH 2.0-2.5 for a four day period at room temperature. After removal from the swelling solution, the hide trimmings were briefly rinsed with water and then subjected to glue extraction while remaining acidulated. The glue was extracted by repetitive water cooks in the presence of excess calcium carbonate to insure neutrality of the solution. Excess calcium .carbonate and insoluble calcium sulfite were removed by centrifugation and the glue liquors were evaporated to give high quality glues.

While in the foregoing specification a number of specific embodiments of this invention have been set forth and various specificdetails have been given, it will be apparent to those skilled in the art that many of the specific embodiments and details can be varied widely without dcparting from the broad idea of the invention.

I claim:

1. A method of extracting animal glue from collagenbearing animal tissues, characterized by the step of carrying out the extraction by contacting collagen-bearing animal tissues with hot water to extract the glue and also contacting said hot water with an insoluble basic substance to maintain said water at a substantially non-acidic pH, saidcollagen-bearing tissues. being acidulated with awater-soluble acid and being maintained interiorly duringsaid extraction at a substantially acidic pH, said watersolubleacid and said water-insoluble basic substance being characterized by reacting to form a water-insoluble salt,

whereby the extraction is facilitated by the acidity of the tissues while the extracted glue is protected from acidicconditions which would impair its viscosity without increasing the inorganic salt content of the extracted glue.

2. In a method for making glue from collagen-bearing animal tissues wherein said tissues are first conditioned to prepare them for the extraction of the glue, the step of.

to prepare it for the extraction of the glue, the step of extracting glue from said conditioned solid pieces of hide glue stock with water containing a water-insoluble basic compound dispersed therein while said solid pieces are maintained interiorly at a pH below 6.5 with a watersoluble acid, said water-insoluble basic compound and said water-soluble acid being characterized by reacting to form a waterdnsolublesalt.

4. The method step of claim 3 in which said insolublebasic compound is an alkaline-earth metal carbonate.

5. The method step of claim 4 in which said watersoluble acid is oxalicacid.

6. The method step of claim 4 in which said alkalineearth metal carbonate is calcium carbonate.

7. The method step of claim 6 in which said watersoluble acid is oxalic acid.

8. In a method for making glue from hide trimmings wherein said trimmings are conditioned to prepare them for extraction of the glue, the steps of acidifying said trimmings by soaking them in water acidulated with a watersoluble acid to a pH from 1.5 to 6.0, separating the acidulated trimmings, and thereafter extracting glue from the acidulated trimmings by contacting them with hot water and also contacting said hot water with a water-insoluble basic compound, said water-soluble acid and said waterinsoluble basic compound being characterized by reacting to form a water-insoluble salt, whereby the extraction is facilitated by the acidity of the tissues while the extracted glue is protected from acidic conditions which would impair its viscosity without increasing the inorganic salt content of the extracted glue.

9. The method steps of claim 8 in which said waterinsoluble basic compound is an alkaline-earth metal carbonate and in which said water-soluble acid is oxalic acid.

10. The method steps of claim 8 in which said waterinsoluble basic compound is calcium carbonate and in which said water-soluble acid is oxalic acid.

11. In a method for making glue from collagen-bearing animal tissues wherein said tissues are conditioned to pre pare them for the extraction of glue, the steps of acidifying said tissues by soaking them in water maintained at a pH below 6.5 with a water-soluble acid, separating the acidulated tissue solids, contacting the acidulated tissue solids with an aqueous solution containing a second watersoluble acid and being at a pH below 6.5 to replace the first-mentioned water-soluble acid within said tissue solids with said second water-soluble acid, separating the tissue solids after the completion of said replacement, and extracting glue from the acidulated solids thus obtained with hot water containing a water-insoluble basic compound dispersed therein while the interior portions of said tissues are at a substantially acidic pH, said first-mentioned watersoluble acid being characterized by forming a water-soluble salt with said water-insoluble basic compound, and said second-mentioned water-soluble acid being characterized by forming a water-insoluble salt with said waterinsoluble basic compound.

12. The method steps of claim 11 in which said firstmentioned water-soluble acid is hydrochloric acid, said second-mentioned water-soluble acid is oxalic acid, and said water-insoluble basic compound is calcium carbonate.

References Cited in the file of this patent UNITED STATES PATENTS 721,852 Arens Mar. 3, 1903 748,866 Hewitt Jan. 5, 1904 1,895,446 Christopher et al. Jan. 31, 1935 2,020,234 Bowman et al. Nov. 5, 1935 2,024,683 Epstein et al. Dec. 17, 1935 2,048,728 Christopher July 28, 1936 2,598,608 Salo et al. May 27, 1952 2,648,659 Spence et al. Aug. 11, 1953 

1. A METHOD OF EXTRACTING ANIMAL GLUE FROM COLLAGENBEARING ANIMAL TISSUES, CHARACTERIZED BY THE STEP OF CARRYING OUT THE EXTRACTION BY CONTACTING COLLAGEN-BEARING ANIMAL TISSUES WITH HOT WATER TO EXTRACT THE GLUE AND ALSO CONTACTING SAID HOT WATER WITH AN INSOLUBLE BASIC SUBSTANCE TO MAINTAIN SAID WATER AT A SUBSTANTIALLY NON-ACIDIC PH, WATER-SOLUBLE ACID AND BEARING TISSUES BEING ACIDULATED WITH A WATER-SOLUBLE ACID AND BEING MAINTAINED INTERIORLY DURING SAID EXTRACTION AT A SUBSTANTIALLY ACIDIC PH, SAID WATERSOLUBLE ACID AND SAID WATER-INSOLUBLE BASIC SUBSTANCE BEING CHARACTERIZED BY REACTING TO FORM A WATER-INSOLUBLE SALT, WHEREBY THE EXTRACTION IS FACILITATED BY THE ACIDITY OF THE TISSUES WHILE THE EXTRACTED GLUE IS PROTECTED FROM ACIDIC CONDITIONS WHICH WOULD IMPAIR ITS VISCOSITY WITHOUT INCREASING THE INORGANIC SALT CONTENT OF THE EXTRACTED GLUE. 